The Nudix hydrolase superfamily is characterized by a highly conserved signature sequence, the "Nudix box" containing 9 amino acids distributed over a span of 23 amino acids as follows: GxxxxxExxxxxxxREUxEExGU (U=Ile.,Leu, or Val) A BLAST search of the data banks reveals over 1000 open reading frames (Orfs) distributed amongst 100 species, containing the Nudix box signature sequence. Many of the genes for these Orfs have been cloned, expressed, and their proteins purified. The proteins are enzymes catalyzing the hydrolysis of a diverse series of substrates having the general structure Nucleoside hence the mnemonic, "Nudix." Depending on the moiety, X, these nucleoside diphosphate derivatives are either (deoxy) nucleoside triphosphates, nucleotide sugars, cell signalling molecules, or coenzymes. The function of these enzymes is to remove potentially toxic materials from cells, to regulate cell signalling molecules, or to modulate the accumulation of metabolic intermediates during the cell cycle. New members of the gene family will be cloned, expressed, and characterized in respect to their particular biochemical reaction, their physiological functions, and their structure - function relationships.